问题
选择题
When I try to understand ________ that prevents so many children from being happy, there seem to be three causes.
A．why it is
B．what it does
C．why it does
D．what it is
答案
D
题目分析：句意：当我试图理解是什么阻止这么多的孩子快乐，似乎有三个原因。这里使用了强调句的特殊问句，因为that后面缺少主语，所以用疑问词what，又因为这个强调句的特殊问句是做understand的宾语从句，所以语序要变成陈述句语序。所以选D。